Continuing innovations in the field of fiberoptic technology have contributed to the increasing number of applications of optical fibers in various technologies. With the increased utilization of optical fibers, there is a need for efficient optical devices that assist in the transmission and the switching of optical signals. At present, there is a need for optical switches that direct light signals from an input optical fiber to any one of several output optical fibers, without converting the optical signal to an electrical signal.
The coupling of optical fibers by a switch may be executed using various methods. One method of interest involves employing a micromirror that is placed in the optical path of an input fiber to reflect optical signals from the input fiber to one of alternative output fibers. The input and output fibers can be either uni-directional or bidirectional fibers. In the simplest implementation of the mirror method, the input fiber is aligned with one of two output optical fibers, such that when the mirror is not placed in the optical path between the two fibers, the aligned fibers are in a communicating state. However, when the mirror is placed between the two aligned fibers, the mirror steers (i.e., reflects) optical signals from the input fiber to a second output fiber. The positioning of the mirror relative to the path of the input fiber can be accomplished by using an apparatus that mechanically moves the mirror. There are number of proposals to using micromachining technology to make optical signals. In general, the proposals fall into two categories: in-plane free-space switches and in-plane guided wave switches. Free-space optical switches are limited by the expansion of optical beams as they propagate through free space. For planar approaches, the optical path length scales linearly with the number of input fibers. Switches larger than 30.times.30 require large mirrors and beam diameters on the order of 1 millimeter (mm). For these planar approaches, the number (N) of input fibers scales linearly with the beam waist and the size of the optical components. Thus, the overall switch size grows as N.sup.2. It is estimated that a 100.times.100 switch would require an area of 1 m.sup.2, which would be a very large switch. Moreover, constraints such as optical alignment, mirror size, and actuator cost are likely to limit the switch to much smaller sizes. One planar approach claims that the optical switch can be designed so that it scales with the optical path difference, rather than the overall optical path. If this is possible, it would certainly allow larger switches. However, the optical path difference also scales linearly with the number of input fibers for a planar approach, so the switch grows very large as it is scaled to large fiber counts.
For guided wave approaches, beam expansion is not a problem. However, loss at each cross point and the difficulty of fabricating large guided wave devices are likely to limit the number of input fibers in such switches.
For both approaches, constraints such as loss, optical component size, and cost tend to increase with the number of fibers. There is a need for an optical cross connect switch which scales better with the number of input and output fibers. Some free-space optical systems can achieve better scaling. These systems make use of the fact that it is possible to use optical steering around in two directions to increase the optical fiber count. Recently, optical switches that use such mirrors have been announced. The systems use piezoelectric elements or magnetically or electrostatically actuated micromirrors. The actuation method for these approaches is often imprecise. To achieve a variable switch, it is typically necessary to use a very high level of optical feedback.
What is needed is a micromachine that enables steering of optical signals from at least one input to a number of alternative outputs, where the arrangement of the outputs is not limited to a linear configuration. What is further needed is a method of fabricating and arranging arrays of the micromachines such that the switching is accurate and repeatable.